Bedding units such as mattresses and box springs conventionally include a plurality of springs defining a load supporting surface whose firmness is selected to suit needs and desires of the customer. For example, heavier people require a firmer unit than do lighter people so as to prevent excessive deflection. Also, different people of the same weight often desire a different firmness for most comfortable sleeping.
Greater firmness of bedding units can be achieved by increasing the diameter wire of the springs that define the load supporting surface. However, this necessarily results in a heavier unit as well as increased cost to the customer. Another way in which greater firmness can be achieved is by the use of an auxiliary panel on the load supporting surface in the central sleeping area at which the greater support is desired.
U.S. Pat. Nos. 3,242,505, 3,735,431 and 3,840,915 disclose bedding units having auxiliary panels for increasing firmness at the central sleeping area. Each of these panels includes straight wires whose ends are connected to a peripheral wire and whose intermediate portions are supported by the springs of the unit in order to provide cooperation of the springs of the unit in supporting any concentrated weight such as from the sleeper's chest or buttocks. During use, these straight wires are loaded in a bending mode and tend to pull the peripheral wire portions of the panel toward each other due to the manner of loading.
U.S. Pat. Nos. 2,383,157 and 4,122,566 disclose bedding unit auxiliary panels with open areas within their peripheral wires such that certain of the springs are not connected to the panels. As such, the degree to which firmness can be increased is limited in units having this type of auxiliary panel.
U.S. Pat. Nos. 2,280,912, 2,386,456 and 2,659,417 disclose spring units including torsion bar springs of one type utilized in accordance with the present invention in a particular way to provide an auxiliary support panel for a bedding unit.